Sikhs and Indians killing each other? why would I care, they can both go to hell for what I care....
If they truly want Khalistan to become an independent state, then it can only be possible through Pakistan, since east Punjab in India is naturally geographical part of west Punjab in Pakistan. If Americans want Khalistan, then they would need Pakistan. But I really don't care about Sikh and their "cause" considering how they back stabbed their own Punjabi fellows who were happen to be Muslims.
If Sikhs unanimously decide to become independent and even be part of Pakistan, all they have to do is just let Pakistan army quietly enter their territory, and then declare independence in UN as a sovereign state.
If Khalistan becomes independent, it would be land locked and may become dependent on Pakistan, eventually it might even become part of Pakistan, and we would have greater Punjab within Pakistan. but seriously? Why would we want bunch of Sikhs in our country, who potentially might back stab us, they are a reliability. But on the positive side, if we ( Pakistan) get control over east Punjab, we can easily have access to Kashmir, and make it an independent state, that way we would have Greater Punjab and Kashmir. India would lose geographical advantage on us, and it would become easier for us to disintegrate India from within that way. As if India is not already divided, all we have to do is give it a little push and it would come falling down, and that will be the end of the lingering British colonial legacy known as India in the subcontinent. We would have a liberated Subcontinent and its states.